The present invention relates to a cathode which is useful in a water photolysis apparatus and, more specifically, to a cathode which improves the efficiency of the water photolysis apparatus.
The evolution of hydrogen and oxygen from a water photolysis apparatus is known. Water photolysis produces a dissociation of water into hydrogen and oxygen by the influence of light on at least one of a pair of semiconductor electrodes. The generated hydrogen can be burned as fuel. With the increasing concern for sources of energy, the water photolysis apparatus has become of increased interest to those in the energy generation field.
A typical prior art water photolysis apparatus includes a titanium dioxide (TiO.sub.2 ) anode and a platinum cathode. This conventional water photolysis apparatus has a maximum quantum yield of oxygen evolution in the range of 80 - 85%, but only about a 20% quantum yield for hydrogen evolution using an applied bias voltage of about 0.9 volt. It has been determined that for proper operation the platinum cathode surface must be between 5 to 50 times the area of the anode surface. The expense of a large platinum cathode and the low hydrogen yield in the conventional water photolysis apparatus contribute to its non-competitiveness as a source of hydrogen. Therefore, it would be most desirable to increase the cathode efficiency to make the water photolysis process more competitive as a means of generating hydrogen fuel.